There are known a variety of devices for popcorn processing, for example, the one taught in U.S. Pat. No. 7,024,986 that describes “a popcorn maker including a self-regulating heating unit. The self-regulating heating unit provides a regulated heat to the popcorn maker. The self-regulating heating unit can be configured to maintain a predetermined temperature for the popcorn maker. The predetermined temperature can be adjusted to provide appropriate amount of heat to the popcorn maker for popping a maximum number of corn kernels while limiting the heat from causing damage to heating coils and thermoplastic parts of the popcorn maker. The self-regulating heating unit includes a positive temperature coefficient heater.”
Another U.S. Pat. No. 5,421,253 teaches a ‘convection oven corn popper and method’ that “ . . . is provided to air-pop popcorn in combination with a convection-type oven. The device comprises a spring-mounted bowl to hold corn kernels and includes a slot in the sidewall for popped popcorn to exit therefrom. The exiting popcorn falls into the cooking chamber of the oven where it is held warm until ready to eat.”
“A portable heat-concentrating kettle cooker” is taught in U.S. Pat. No. 6,234,064, in particular, having “a housing with a burner supported within the housing and a kettle carrier pivotably attached to a top edge of the housing such that it can be pivoted from a substantially horizontal position across the top of the housing to a substantially vertical position. The kettle carrier includes a cooking kettle that is positioned over the burner when the kettle carrier is in its substantially horizontal position, and when the kettle carrier is in its substantially vertical position, the cooker kettle is positioned to empty its contents into a tub that is supported next to the housing by a detachable frame extending from the housing. Additional features of the cooker include a heat intensification chamber formed by a wall around the burner in order to redirect radiant energy from the burner back into the heat intensification chamber. A cooking oil receptacle is also detachably mounted to the housing. Fuel supplied to the heater can be natural gas, propane, or electricity, with fuel supply lines passing through a fuel supply/control chamber at the front of the housing and fuel regulating controls positioned on the front of the housing.”
As believed, a related art device, being the closest to the present invention, is taught in U.S. Pat. No. 4,727,798 issued to Nakamura (herein further called ‘Nakamura’) that discloses a “popcorn processing machine has a heating chamber into which a measured quantity of raw corn kernels are fed in each operational cycle to be heated, agitated, and thus popped by only a hot air supplied under pressure as a whirling rising vortex, without the use of an oil, whereby greatly expanded puffs of popcorn of uniform quality are produced in a high yield and in a short processing time. The bottom of the heating chamber can be opened by a simple mechanism, whereby the popped popcorn product can be quickly dumped and the chamber bottom rapidly reclosed, the operational cycle time thereby being extremely short.”
Designers of popcorn making machines often encounter a common problem particularly described in Nakamura: “In a typical popcorn processing machine known heretofore, a receiving dish or pan into which corn kernels are charged is provided above a heat source. At the bottom of this pan, agitator vanes for rotating along the upper surface of the pan bottom are fixedly supported on a vertical shaft. Accordingly, when the vertical shaft is rotated, the vanes rotate within the pan thereby to agitate the raw corn kernels as they are heated by the heat source, whereby the corn kernels are heated and popped into expanded state to fill the interior of the pan. In such a machine, oil is ordinarily placed in the pan in order to cause the raw corn kernels to pop rapidly. As a consequence of the agitation of the corn kernels, this oil tends to be scattered together with minute particles of the corn against the inner surface of a transparent cover installed for observation around the sides of the pan. The oil and corn particles thus adhere to the glass cover, thereby dirtying the glass and causing it to become opaque. Furthermore, if these contaminants are left in adhering state, they will attract undesirable insects such as cockroaches and are therefore very unhygienic. Since an opaque condition of the glass cover prevents or obstructs observation of the corn popping progress, the contaminants must be frequently wiped off by hand, which is an inconvenient task. However, if oil is not used in order to prevent this contamination, the time for popping the raw corn becomes disadvantageously long. Furthermore, the construction of the machine itself in this case has been complicated because of the necessity of providing rotational support means and driving means for the agitator vanes.”
As shown above, Nakamura solves this problem by supplying “a hot air supplied under pressure as a whirling rising vortex, without the use of an oil” into the heating chamber with an openable bottom for popping. Thereafter, “the popped popcorn product can be quickly dumped and the chamber bottom rapidly reclosed, the operational cycle time thereby being extremely short.” However, the “whirling rising vortex” conditions an increased density of kernels in the lower central region of the chamber, wherein the speed of kernels and temperature of hot air are essentially minimal, which leads to uneven heating the kernels located in this region that slows down the overall heating of corn kernels in the chamber thereby decelerating the whole process of popcorn preparation. Besides, the movable bottom of the heating chamber reduces the overall reliability and maintainability of the Nakamura's machine.